1. Field of the Invention
The invention relates to a superconductor YBa.sub.2 Cu.sub.3 Ox and to a process for manufacturing the superconductor YBa.sub.2 Cu.sub.3 Ox, and more particularly, to a process using an infiltration-reaction technique for manufacturing the superconductor YBa.sub.2 Cu.sub.3 Ox, hereinafter referred to as 123, having improved electrical and mechanical properties by distributing Y.sub.2 BaCuO.sub.5, hereinafter referred to as 211, grains as pinning centers and substantially eliminating pores and residual liquid phase from the final product.
2. Background Information
Although 123 superconductors have a higher Tc (critical temperature) than other conventional metallic superconductors like Nb.sub.3 Sn and Nb.sub.3 Ge, it is difficult to put 123 superconductors to practical use due to their lower Jc (critical current density). The reason for the lower Jc is that magnetic fluxes penetrate into the 123 superconductor and move through the 123 superconductor when a magnetic field larger than Hcl (low critical magnetic field) is applied. In order to control the motion of the magnetic fluxes, it is essential to distribute pinning centers inside the 123 superconductor. The pinning centers hold or fix the penetrating magnetic fluxes so they do not move through the 123 superconductor. Of the many possible pinning centers, 211 grains are known to be the most effective in 123 superconductors.
In conventional methods, 123 superconductors, with 211 grains distributed as pinning centers, are manufactured by first decomposing a 123 powder compact into 211 grains and a liquid phase by heat treatment at 1000-1200 degrees celsius. The resulting mass is then cooled down to below 1000 degrees celsius so that the 123 superconductor is formed by the peritectic reaction between the 211 grains and the liquid phase.
When the peritectic reaction is initiated, 123 grains are nucleated on the surface of the 211 grains and grow entrapping the 211 grains. After the peritectic reaction is completed, 123 superconductor is present where the 211 grains are distributed. However, in the conventional process a residual liquid phase(s) and pores remain. The residual liquid phase(s) cannot further react with the 211 grains trapped inside the 123 grains since the 211 grains are isolated by the 123 grains from the residual liquid phase. The presence of the residual liquid phase and the closed pores deteriorate the electrical and mechanical properties of the 123 superconductor. The 123 superconductor produced by conventional methods has a volume percent of 211 grains distributed as pinning centers inside the 123 superconductor of only a maximum of about 25 volume percent.
For further explanation see: Murakami et al, "Microstructural Study of the Y-Ba-Cu-0 System At High Temperatures", Japanese Journal of Applied Physics, Vol. 28, No. 3, pp. L 399-L 401, March 1989; publication of ICMC '90 Topical Conference, "High-Temperature Superconductors, Materials Aspects", May 9-11, 1990, Garmisch-Partenkirchen, Fed. Rep. of Germany; and Murakami et al, "A New Process with the Promise of High Jc in Oxidek Superconductors", Japanese Journal of Applied Physics, Vol. 28, No. 7, pp. 1189-1194, July 1989, each of which are incorporated herein by reference as if fully set forth hereat.
Therefore, the present invention improves the electrical and mechanical properties of the 123 superconductor by evenly distributing the 211 grains as pinning centers and by substantially eliminating the presence of the residual liquid phase and the closed pores from the 123 superconductor.
It is an object of the present invention to manufacture a 123 superconductor having 211 grains evenly distributed as pinning centers to increase the Jc.
It is another object of the present invention to manufacture a 123 superconductor substantially absent any closed pores thereby enhancing the electrical and mechanical properties of the 123 superconductor.
It is another object of the present invention to manufacture a 123 superconductor substantially absent any residual liquid phase thereby enhancing the electrical and mechanical properties of the 123 superconductor.
It is another object of the present invention to manufacture a 123 superconductor a density of over 95 volume percent of the theoretical density and a volume percent of 211 grains evenly distributed as pinning centers inside the 123 superconductor of in the range of about 40 to 60 volume percent.
It is another object of the present invention to manufacture a 123 superconductor having a .DELTA.M of as large as 56 emu/cc at zero applied field and 30 emu/cc at 1000 Oe applied field.
The preceding objects should be construed as merely presenting a few of the more pertinent features and applications of the invention. Many other beneficial results can be obtained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to both the Summary of the Invention and the Detailed Description, below, which describe the preferred embodiment in addition to the scope of the invention defined by the claims considered in conjunction with the accompanying drawings.